If you love books, be glad you live in this era.
There was a time when the best available writing materials were papyrus (interlocking strips cut from reedy plants) and parchment (the hides of sheep and cattle). Since papyrus and parchment were scarce and expensive, it was not uncommon for scholars to recycle materials by scraping off text and starting over. The practice was so common that a word was coined for it: palimpsest, meaning “a manuscript with multiple sets of overlaid text.”
“Overlaid text” was the key: Traces of the original writing were always left behind. Today, state-of-the-art imaging technology can expose that writing. A group of students at the Rochester Institute of Technology (RIT) recently developed an ultraviolet-fluorescence imaging system to reveal handwriting hidden beneath a 15th-century script. Specifically, they examined a page from a Book of Hours, a devotional text popular with lay Christians during the Middle Ages. Their process showed the remains of an elegant French cursive script beneath the visible text, left after the page was presumably scraped clean and reused by European monks at about 1450 A.D.
Unfortunately, this volume has been victimized by the controversial practice of cutting pages from medieval manuscripts and selling them individually. Further research in this case will depend upon locating and gaining access to 29 other pages known to exist from this book.
But at least now they have a tool to unlock secrets that have been invisible for hundreds of years.
For a more thorough description, see “College Sophomores Discover Hidden Text in Medieval Manuscript” by Nora McGreevy at https://www.smithsonianmag.com/smart-news/students-discover-hidden-text-medieval-manuscript-180976385/?. The photo came from that site.